i'm trying to build some userdefined actions, which should iterate an array and pass the values as stings to a child step.
i need some help to understand how an action in VisualBuild enters a child step and, once finshed with it, loops back to the parent step.

To implement looping, you would need to configure the step's build rule in such a way that it would process all strings in the array (similar to how the looping samples in Advanced.bld and Misc.bld work). Keep in mind that a new instance of the step is created/destroyed for each iteration, so you would need to store the array data in a VBP temporary macro.

Much of the logic for repeating of build rules (for non-Process Files actions) and the Process Files action is built into the builder component, so it's not currently possible to create a user-defined action that uses some other type of iterating functionality.

See 'user actions' in the help index for details on creating user-defined actions, and also the samples in the Samples\User Actions folder. See 'object model' for details on the COM objects and properties that are available from a user-defined action.